1. Field of the Invention
The present invention relates to a fuel pump to be actuated by engine power.
2. Description of Related Art
Japanese Laid-Open Publication No. 2000-282994 discloses a prior art fuel pump which utilizes rotation of an eccentric cam by an engine by converting the rotation of the eccentric cam into reciprocating motion of a piston. FIG. 6 of the accompanying drawings shows such a fuel pump 10, and FIG. 7 shows a detailed cross section of essential parts of the fuel pump shown in FIG. 6. The fuel pump 10 includes a bottom body part 14 which is fixedly attached to a cylinder head cover 12 of an engine, a top body part 16 mounted on the bottom body part 14, a cover 18 on the top body part 16, and a piston 20 reciprocally mounted in the bottom body part 14. As shown in FIG. 6, the cover 18 is positioned on top of the top body part 16, and the bottom body part 14 is mounted under the top body part 16.
The fuel pump 10 is to be arranged with a rotary shaft 22 positioned below the piston 20 and having an eccentric cam 24. The shaft 22 is rotated by engine power, and the eccentric cam 24 is positioned at a tip of the piston 20. A piston spring 26 is provided between the piston 20 and the bottom body part 14, and urges the piston 20 toward the eccentric cam 24 so the piston remains in contact with the eccentric cam 24. The piston 20 thus vertically reciprocates in the bottom body part 14 in response to the rotation of the eccentric cam 24.
A diaphragm assembly 30 is coupled to the piston 20, and includes a diaphragm 28 and a rod 32 coupled to the diaphragm 28. An engagement member 36 has an elongated hole 34 along an axis thereof, and is fixedly attached to a tip of the rod 32. Further, a pin 38 is fixedly attached to the piston 20, and fits in the elongated hole 34 of the engagement member 36.
The diaphragm 28 is sandwiched between the bottom body part 14 and the top body part 16, and a seal such as a gasket is sandwiched between the top body part 16 and the cover 18. In this state, the bottom body part 14, the top body part 16 and the cover 18 are fixed together using a bolt 42. A pump chamber 44 is defined by the top body part 16 and the diaphragm 28, and is present near the top body part 16. A diaphragm spring 46 is provided between the bottom body part 14 and the diaphragm 28 in order to continuously urge the diaphragm 28 toward the pump chamber 44 (i.e. toward a pump chamber pressurizing position).
An intake chamber 48 and a discharge chamber 50 are independently defined by the top body part 16 and the seal 40. An intake path 52 is formed in the top body part 16 in order to connect the intake chamber 48 to the pump chamber 44, and the intake path is opened and closed by an intake (one-way) valve 54. Further, the top body part 16 has a discharge path 56 formed therein in order to connect the discharge chamber 48 to the pump chamber 44. The discharge path 56 is opened and closed by a discharge (one-way) valve 58.
In the fuel pump 10, the piston 20 vertically reciprocates in response to the rotation of the eccentric cam 24 fixedly attached around the shaft 22. When both the piston 20 and the diaphragm 28 are moved downward as shown in FIG. 6, the discharge. valve 58 closes the discharge path 56. At the same time, the intake valve 54 is opened, so that fuel is introduced into the pump chamber 44 from the intake chamber 48 via the intake path 52. Thereafter, when the piston 20 and the diaphragm 28 move upward, the intake valve 54 closes the intake path 52, and the discharge valve 58 opens the discharge path 56, so that the fuel is introduced into the discharge chamber 50 from the pump chamber 44.
The piston spring 26 must be sufficiently strong so as to maintain the piston 20 continuously in contact with the eccentric cam 24 so that the piston 20 reliably follows the rotating eccentric cam 24. The piston spring 26 is required for the downward movement of the diaphragm 28 toward a depressurizing position to effect a fuel intake action, and thus must have sufficient strength to overcome the resilient biasing force of the diaphragm spring 46 which resists the downward movement of the diaphragm 28. Further, the larger the diaphragm 28, the stronger must be the resiliency of the piston spring 26. Still further, the more resilient the piston spring 26 must be, the more expensive of a material is generally required to form the piston spring, which inevitably makes the piston spring more expensive.
If the piston spring 26 is weakened, the piston 20 will sometimes fail to follow the eccentric cam 24. In such a case, undesirable noises may be caused due to improper interaction between the piston 20 and the eccentric cam 24. When the piston spring 26 is strengthened in order to overcome this problem, the pin 38 fixedly attached to the piston 20 may strike against the engagement member 36 fixedly attached to the rod 32, thereby causing significant shocks and perhaps large knocking noises. Such striking contact will cause damage to the pin 38 at the contact point, as well as to the diaphragm 28 and components adjacent the rod 32.
In order to overcome the foregoing problems of the related art, the present invention is intended to provide a fuel pump which does not require expensive material for a piston spring, reduces knocking noises and protects components near colliding portions against damage.
According to the invention, there is provided a fuel pump for pumping fuel in response to rotation of an eccentric cam, the fuel pump comprising: a fuel pump body having a pump chamber; a pumping member-movably provided at the pump chamber for pressurizing and depressurizing the pump chamber, the pumping member being movable between a first pumping member position and a second pumping member position; a piston movably mounted to the fuel pump body and being arranged to be operably engaged with the eccentric cam for movement between first and second ends of a piston stroke, the piston being operably coupled to the pumping member so that the pumping member is caused to move toward the first pumping member position due to the piston moving toward the first end of the piston stroke, and toward the second pumping member position due to the piston moving toward the second end of the piston stroke; a piston-following spring operably engaged with the piston to urge the piston toward the first end of the piston stroke; and a pumping member-moving spring operably engaged with the pumping member to urge the pumping member toward the first pumping member position.
The fuel pump further includes a pumping member spring mechanism urging the pumping member toward the second pumping member position, and the pumping member preferably comprises a diaphragm.
The fuel pump body comprises a first fuel pump body part, and a second fuel pump body part secured to the first fuel pump body part; and the diaphragm is sandwiched between the first and second fuel pump body parts.
The fuel pump further preferably includes a first engagement member coupled to the diaphragm; a second engagement member provided at the piston and being arranged for engagement with the first engagement member; and a plate member positioned between the first engagement member and the pump member-moving spring so as to be urged by the pump member-moving spring toward the first engagement member. The second engagement member is engageable with the first engagement member to limit an amount of movement of the first engagement member relative to the piston. Further, a rod preferably couples the first engagement member to the pumping member; the first engagement member comprises a pin fixed to the rod; and the second engagement member comprises an elongated groove provided in the piston, the pin being movably engaged in the elongated groove. The plate member is preferably an annular plate disposed about the rod and between the pin and the pumping member-moving spring. The pumping member-moving spring and the piston-following spring are preferably disposed one within the other and about the rod.
In the preferred form of the invention, the fuel pump body has defined therein the pump chamber, an intake chamber and a discharge chamber; the pump chamber is bounded by the pumping member; the intake chamber is connected to the pump chamber via a first one-way valve; and the discharge chamber is connected to the pump chamber via a second one-way valve. The first one-way valve allows flow in a direction from the intake chamber to the pump chamber; and the second one-way valve allows flow in a direction from the pump chamber to the discharge chamber.